On the Conjunctiva
The conjunctiva is the clear tissue that covers the white part of the eyeball. There are cells that contain pigment located in the conjunctiva. These cells can produce excessive pigment and cause brown spots in the eye. The British Journal of Ophthalmology report that these spots should be examined regularly by an eye care practitioner as up to 30 percent of them can become cancerous.
On the Sclera
The sclera is the white part of the eyeball. A bluish-brown spot can appear in the sclera. It is known as a Nerve Loop of Axenfeld. These are simply anatomical structures, and pose no health risk.
On the Cornea
The cornea is the clear covering that is over the iris and pupil. A brown spot on the cornea is generally from a foreign body that needs to be removed, or it may be from rust from a previously removed metallic foreign body.
On the Iris
The iris, or colored part of the eye, can have brown spots that are dangerous and some that are not. Excessive iris pigment may cluster in one area of any color iris and cause a dark spot. Specific formations of pigment can indicate eye health problems that may require immediate treatment.
What To Do
There are too many possibilities of brown spots on the eye to list them all. The list and descriptions above are some of the more common examples. If someone has a brown spot on their eye, it should be evaluated by an optometrist or an ophthalmologist to ensure that it does not pose a health risk to the eye.